Laboratory Studies

Urinalysis

The presence of dysmorphic red blood cells (RBCs), albumin, or RBC casts suggests glomerulonephritis as the cause of renal failure. Waxy or broad casts are observed in all forms of chronic kidney disease (CKD), including chronic glomerulonephritis. Low urine specific gravity indicates loss of tubular concentrating ability, an early finding in persons with CKD. See Urinalysis.

Urinary protein excretion

Urinary protein excretion can be estimated by calculating the protein-to-creatinine ratio on a spot morning urine sample. The ratio of urinary protein concentration (in mg/dL) to urinary creatinine (in mg/dL) reflects 24-hour protein excretion in grams. For instance, if the spot urine protein value is 300 mg/dL and the creatinine value is 150 mg/dL, the protein-to-creatinine ratio is 2. Thus, in this example, the 24-hour urine protein excretion is 2 g.
[11]

The estimated creatinine clearance rate is used to assess and monitor the glomerular filtration rate (GFR). The 2 formulas available for calculation of the GFR are the Cockcroft-Gault formula, which estimates creatinine clearance, and the Modification of Diet in Renal Disease (MDRD) Study formula, which is used to calculate the GFR directly.

The Cockcroft-Gault formula is simple to use but overestimates the GFR by 10-15% because creatinine is both filtered and secreted. The MDRD formula is much more complex but can be determined with a smartphone and tablet application available from the National Kidney Foundation or can be calculated online through the Hypertension, Dialysis, and Clinical Nephrology Web site.

The estimated creatinine clearance rate is also used to monitor response to therapy and to initiate an early transition to renal replacement therapy (eg, dialysis access placement and transplantation evaluation). The degree of proteinuria, especially albuminuria, helps predict the renal prognosis in patients with chronic glomerulonephritis. Patients with proteinuria exceeding 1 g/day have an increased risk of progression to end-stage renal failure.

Complete blood count

Anemia is a significant finding in patients with some decline in the GFR. Physicians must be aware that anemia can occur even in patients with serum creatinine levels lower than 2 mg/dL. Even severe anemia can occur at low serum creatinine levels. Anemia is the result of marked impairment of erythropoietin production.

Serum chemistry

Serum creatinine and urea nitrogen levels are elevated. Impaired excretion of potassium, free water, and acid results in hyperkalemia, hyponatremia, and low serum bicarbonate levels, respectively. Impaired vitamin D-3 production results in hypocalcemia, hyperphosphatemia, and high levels of parathyroid hormone. Low serum albumin levels may be present if uremia interferes with nutrition or if the patient is nephrotic.

Levels of fibroblast growth factor 21 (FGF21) have been found to be significantly elevated in patients with CKD
[12] and the high levels of FGF21 may explain the excess overall and cardiovascular mortality in patients with CKD. These adverse effects of elevated FGF21 are not clearly understood but research is under way to elucidate its biologic effects.

Next:

Other Studies

Renal ultrasonography

Obtain a renal ultrasonogram to determine renal size, to assess for the presence of both kidneys, and to exclude structural lesions that may be responsible for azotemia. Small kidneys often indicate an irreversible process.

Kidney biopsy

If the kidney is small, kidney biopsy is usually unnecessary; no specific pattern of disease can be discerned at this point. A kidney biopsy may be considered in the minority of patients who exhibit an acute exacerbation of their chronic disease. This may be particularly pertinent to patients with preserved kidney size and in those with lupus nephritis.

In early stages, the glomeruli may still show some histologic evidence of the primary disease. In advanced stages, the glomeruli are hyalinized and obsolescent. The tubules are disrupted and atrophic, and marked interstitial fibrosis and arterial and arteriolar sclerosis occur.

Photomicrograph of a kidney biopsy from a patient with crescentic glomerulonephritis showing prominent fibrocellular crescent formation and moderate mesangial proliferation in a glomerulus. Hematoxylin and eosin stain. Image courtesy of Wikipedia.